Mystery Service Station

While standing in line at the PNC Bank on Beverly Road this morning, I turned around and looked at the auto repair shop across the street from the bank. I've always wondered about the place because it doesn't have any signs on it at all, yet it's always packed and they are always working in there.

Anyone care to share any info on the place? They must be really good if they don't even advertise their name on the building. How do people get their cars worked on? Do they just walk in or is it referral only?